The contamination chain
A compressor does not create purity: it draws in atmospheric air and concentrates the contaminants it contains. Learn about the four main contaminants that affect compressed-air quality.
Water
Present as vapor, aerosol, or liquid. It can cause corrosion, valve failures, and blemishes in painting processes.
Oil
It may come from compressor lubricant or the surrounding environment, impairing adhesion and contaminating products and processes.
Particles
Dust, rust, and desiccant material can cause blockages, abrasion, and surface defects.
Microorganisms
Bacteria and fungi may proliferate in humid conditions and pose a risk to sensitive processes.
Understanding ISO 8573-1
The classification covers three independent dimensions: particles, water, and oil. A specification is stated in the format [Particles : Water : Oil], for example: Class 1:2:1.
| Class | 0,1 a 0,5 µm (nº/m³) | 0,5 a 1,0 µm (nº/m³) | 1,0 a 5,0 µm (nº/m³) |
|---|---|---|---|
| 0 | As specified by the user, more stringent than Class 1 | ||
| 1 | ≤ 20.000 | ≤ 400 | ≤ 10 |
| 2 | ≤ 400.000 | ≤ 6.000 | ≤ 100 |
| 3 | Not specified | ≤ 90.000 | ≤ 1.000 |
Compressor technologies
No single compressor is ideal for every application. Selection depends on the demand profile, pressure, purity requirement, and energy cost.
Reciprocating piston
Low to medium flow, high pressure, and intermittent operation.
High pressure differential and robust construction.
Pulsation, noise, and valve maintenance.
Oil-injected rotary screw
Continuous operation and medium flow, typically between 5 and 13 bar.
Steady flow and a good performance-to-cost ratio.
Potential oil carryover.
Dry oil-free rotary screw
Critical processes and continuous operation.
No oil in the compression chamber.
Higher initial investment and greater sensitivity to operating conditions.
Centrifugal
High flow rates and a stable base demand.
Oil-free compression and high efficiency at the design point.
Limited turndown and surge risk outside the operating envelope.
Dryers and water removal
Selection starts with the lowest pressure dew point (PDP) required at the critical point. Each technology has an appropriate operating range.
| Technology | Typical PDP | Energy / purge | Application |
|---|---|---|---|
| Refrigerated (non-cycling/cycling) | +3°C a +10°C | Refrigeration compressor / varies with load | Indoor industrial air; not suitable for lines below 0°C. |
| Heatless adsorption | -40°C ou -70°C | Significant dry-air purge consumption | Instrumentation, cold environments, and critical processes. |
| Heat of compression | ≈ -40°C | Uses heat from an oil-free compressor | Stable load, no purge-air consumption, and high energy efficiency. |
| Membrane | Variable | Continuous air purge | Point-of-use, hazardous areas, and applications requiring no moving parts. |
Quick tool
Pressure-drop estimate
Pipe diameter has a strong influence on pressure drop. Undersized piping may require a higher compressor discharge pressure and unnecessarily increase energy consumption.
DOE rule of thumb: increasing discharge pressure by 2 psi may raise energy consumption by up to 2%.
* Values are for illustration only. Detailed design requires compressible-flow calculations and validation of actual operating conditions.
Gooseneck take-off and distribution network
Network design is critical to air quality at the point of use. A take-off from the bottom of the main can carry condensate to downstream equipment.
Construction detail — gooseneck take-off
The take-off should leave from the top or upper quadrant of the main, rise slightly, and then descend to the user, creating a physical barrier against liquid-water carryover.
Ring main
Ring mains feed points of use from two directions, helping reduce air velocity, stabilize pressure during peak demand, and isolate sections for maintenance.
Need support sizing your system?
Prime Products engineering provides flow diagnostics, air-quality assessment against defined requirements, and network design to support plant efficiency.
Request an assessment